Active implantable medical devices use batteries to power their functionality. Batteries, however, have limited output capabilities, calling for reduced current consumption wherever possible. Such devices may include circuitry performing various different functions, including, for example, radio telemetry, therapeutic outputs, biological signal processing, alarm generation, memory storage, logic and other operations. This combination of several circuits can require provision of numerous reference voltages within a single device.
Independently creating such reference voltages can be highly power consumptive. For example, band-gap reference voltages may consume power on a constant basis. Zener diodes require a threshold level of current to operate in a stable zone. As a result, the number of independent references provided should be kept to a minimum to preserve power capacity.
A single voltage reference can be used to generate other references using multiplier or divider circuits. An example can be seen in U.S. Pat. No. 8,330,536, which shows a voltage divider providing several output voltage references in FIG. 2 of the patent.
For another example, FIG. 1 of the present disclosure illustrates the prior art use of a resistive divider circuit (first resistor R1 and second resistor R2) to generate a second reference voltage VRef2 from a first reference voltage VRef1. The problem is that this requires current flow through the resistors. Even with very large resistors, the current drawn will, over time, be a drain on the battery. Lower power alternatives are sought.